[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 171805
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU SEP 17 2015

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE
EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE
IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL
ANALYSIS.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...SPECIAL FEATURES...

TROPICAL DEPRESSION NINE IS CENTERED NEAR 16.1N 45.2W AT 17/1500
UTC OR ABOUT 931 NM E OF THE LESSER ANTILLES...MOVING NW AT 5
KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB. MAXIMUM
SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40 KT. SCATTERED
MODERATE CONVECTION IS WITHIN 300 NM E OF THE DEPRESSION CENTER
FROM 10N TO 23N. SEE THE LATEST NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.

A 1008 MB LOW IS SW OF THE CAPE VERDE ISLANDS CENTERED NEAR
12N33W...MOVING W-NW 10 KT OVER THE PAST 24 HOURS. SCATTERED
MODERATE CONVECTION IS FROM 05N TO 15N BETWEEN 30W AND 40W.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE CONDUCIVE FOR A
TROPICAL DEPRESSION TO DEVELOP DURING THE NEXT DAY OR TWO. THERE
IS A HIGH CHANCE OF TROPICAL FORMATION OVER THE NEXT 48 HOURS.

...TROPICAL WAVES...

A TROPICAL WAVE IS IN THE WEST CARIBBEAN WITH AXIS NEAR
80W...MOVING WEST AT 20 KT OVER THE PAST 24 HOURS. CIRA LAYER
PRECIPITABLE WATER IMAGERY INDICATE THE WAVE IS ASSOCIATED WITH
MODERATE MOISTURE FROM THE SURFACE TO 850 MB THAT ENHANCES
SCATTERED MODERATE CONVECTION AND ISOLATED TSTMS AHEAD OF THE
WAVE AXIS...INCLUDING THE COASTLINES FROM EASTERN HONDURAS TO
NORTHERN PANAMA. SIMILAR CONVECTION IS S AND SE OF THE WAVE AXIS
S OF 11N BEING ENHANCED BY THE EPAC MONSOON TROUGH.

...ITCZ/MONSOON TROUGH...

NO MONSOON TROUGH AND/OR ITCZ WAS NOTED OVER THE TROPICAL ATLC
WATERS. OTHER THAN THE CONVECTION ASSOCIATED WITH THE INVEST
AREA AL95 AND THE TROPICAL DEPRESSION NINE DISCUSSED IN THE
SPECIAL FEATURES SECTION...A SURFACE TROUGH EXTENDS FROM 08N19W
TO 15N23W SUPPORTING SCATTERED MODERATE CONVECTION FROM 09N TO
15N BETWEEN 20W AND 28W.

...DISCUSSION...

GULF OF MEXICO...

BROAD SURFACE HIGH PRESSURE COVERS THE EASTERN CONUS AND A
PORTION OF THE W ATLC...EXTENDING A RIDGE ACROSS THE NORTHERN
GULF AND FLORIDA PENINSULA. SOUTH OF THE RIDGE AND OVER THE
EASTERN GULF...A 1012 MB LOW IS ANALYZED NEAR 26N84W WITH
ASSOCIATED TROUGH EXTENDING FROM TAMPA TO THE LOW CENTER TO THE
YUCATAN CHANNEL NEAR 21N86W. THIS AREA OF LOW PRESSURE IS
INTERACTING WITH AN UPPER LEVEL TROUGH...THUS SUPPORTING
CLOUDINESS...SHOWERS AND TSTMS E OF A LINE FROM 30N84W TO
23N88W...INCLUDING THE FLORIDA PENINSULA. THIS WEATHER SYSTEM IS
EXPECTED TO CONTINUE A NE TRACK AND CONTINUE TO PRODUCE HEAVY
RAINFALL ACROSS PORTIONS OF FLORIDA THROUGH FRIDAY. STRONG
SUBSIDENCE AND DRY STABLE AIR WITH CLEAR SKIES COVERS THE
REMAINDER GULF. OVER THE NE GULF...WHERE THERE IS A TIGHTER
PRESSURE GRADIENT WINDS ARE NE TO E OF 15-20 KT. VARIABLE WINDS
OF LESS THAN 15 KT COVER THE REMAINDER BASIN.

CARIBBEAN SEA...

SCATTERED SHOWERS AND TSTMS ARE OVER THE EASTERN PORTION OF THE
YUCATAN CHANNEL EXTENDING TO WESTERN CUBA AND ADJACENT WATERS IN
ASSOCIATION WITH A BROAD LOW PRESSURE SYSTEM OVER THE EASTERN
GULF OF MEXICO. OVER THE S-SW CARIBBEAN...A TROPICAL WAVE AND THE
MONSOON TROUGH ENHANCE SIMILAR CONVECTION. SEE TROPICAL WAVES
SECTION FOR FURTHER DETAILS. AN UPPER LEVEL LOW IS CENTERED OVER
NW HAITI THAT ALONG WITH SHALLOW MOISTURE SHOWN BY SSMI TPW
IMAGERY SUPPORT SCATTERED SHOWERS AND TSTMS ACROSS HISPANIOLA
AND ADJACENT WATERS. THE UPPER LOW IS GENERATING A DIFFLUENT
ENVIRONMENT OVER PUERTO RICO SUPPORTING SIMILAR CONVECTION OVER
CENTRAL AND WESTERN PORTIONS OF THE ISLAND. STRONG DEEP LAYER
WIND SHEAR AND DRY AIR SUPPORT FAIR WEATHER ELSEWHERE ACROSS THE
BASIN. THE TROPICAL WAVE WILL MOVE ACROSS CENTRAL AMERICA FRIDAY
TO SATURDAY. A LOW PRESSURE CENTER WILL DEVELOP OVER THE SW
BASIN FRIDAY MORNING...CONTINUING THROUGH THE WEEKEND.

...HISPANIOLA...

AN UPPER LEVEL LOW IS CENTERED OVER NW HAITI THAT ALONG WITH
SHALLOW MOISTURE SHOWN BY SSMI TPW IMAGERY SUPPORT SCATTERED
SHOWERS AND TSTMS ACROSS HISPANIOLA AND ADJACENT WATERS.
SHOWER/THUNDERSTORM ACTIVITY ASSOCIATED WITH THIS UPPER LEVEL
FEATURE IS FORECAST TO CONTINUE THROUGH SAT.

ATLANTIC OCEAN...

THE MAIN FEATURES IN THE BASIN ARE TROPICAL DEPRESSION NINE AND
AN INVEST AREA EAST OF IT...DISCUSSED IN THE SPECIAL FEATURES
SECTION. A SURFACE TROUGH IS E OF THE INVEST AREA FROM 08N19W TO
15N23W SUPPORTING SCATTERED MODERATE CONVECTION FROM 09N TO 15N
BETWEEN 20W AND 28W. OVER THE SW N ATLC...A SURFACE TROUGH IS
ANALYZED FROM 30N78W TO 24N79W. A DIFFLUENT ENVIRONMENT ALOFT
OVER THIS REGION ALONG WITH LOW LEVEL MOISTURE SUPPORT SCATTERED
MODERATE CONVECTION AND TSTMS N OF 23N W OF 72W. OVER THE NORTH
CENTRAL BASIN...THE TAIL OF A COLD FRONT EXTENDS FROM 30N51W TO
28N59W. A PRE-FRONTAL TROUGH EXTENDS FROM 30N50W TO 23N51W.
THESE TWO FEATURES ENHANCES ISOLATED SHOWERS AND TSTMS N OF 26N
BETWEEN 48W AND 57W. WEAK HIGH PRESSURE DOMINATES OVER THE E
ATLC WATERS. WEAK HIGH PRESSURE OVER THE NW ATLC WILL PERSIST
THROUGH THE WEEKEND. A TROUGH WILL BUILD IN W ATLC BEGINNING
TODAY BECOMING MORE NE/SW ORIENTED ACROSS NW WATERS FRI NIGHT.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
NR
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